Air Density Calculator

This simple GUI allows the user to:

• calculate air density \( \big(\rho\big) \) in kg/m³

by providing the following information:

• air temperature \( \big(T\big) \) in degrees Celsius
• air pressure \( \big(p\big) \) in Pascal
• relative humidity \( \big(\phi\big) \) in %

Relative humidity can be left blank if desired.

If relative humidity is not provided, then the ideal gas law is used:

\[ \rho = \frac{p}{\big(T+273.15\big)\cdot R_d} \]

\( R_d=287.058J/(kg\cdot K) \) is the specific gas constant of dry air.

As can be seen, the temperature \( \big(T\big) \) must be converted into Kelvin.

If relative humidity is provided, then the equation for air density has an additional term:

\[ \rho = \frac{p}{\big(T+273.15\big)\cdot R_d} + \frac{p_v}{\big(T+273.15\big)\cdot R_v} \]

\( R_v=461.5J/(kg\cdot K) \) is the specific gas constant of water vapour.

The vapour pressure of water \( \big(p_v\big) \) can be found from:

\[ p_v = \phi \cdot 6.1078 \cdot 10^{\frac{7.5T}{T+237.3}} \]